Does an optimally foraging oystercatcher obey the functional response?

Area of Science:

• Behavioral ecology
• Predator-prey dynamics
• Foraging theory

Background:

• Optimal foraging theory predicts how animals maximize energy intake.
• Prey depth influences handling time and profitability for predators.
• Oystercatchers (Haematopus ostralegus) are generalist predators feeding on bivalves.

Purpose of the Study:

• To experimentally test the optimal diet model in oystercatchers.
• To investigate how prey depth affects foraging decisions.
• To determine if functional response models accurately describe oystercatcher intake rates.

Main Methods:

• Oystercatchers were presented with bivalves (Scrobicularia plana) at varying depths.
• Handling and search times were recorded as a function of prey depth.
• Prey depth selection and intake rates were observed at different prey densities.

Main Results:

• Handling time increased with bivalve burial depth, reducing prey profitability.
• Observed depth selection matched predictions at low prey densities.
• At high densities, intake rates exceeded predictions, suggesting ignored prey.

Conclusions:

• Oystercatcher foraging depth selection aligns with optimal diet predictions at lower densities.
• Standard functional response models do not fully capture oystercatcher intake rates due to density-dependent factors.
• A multi-species functional response may be required for optimally feeding predators.